The present invention is directed to a process of producing nitroparaffins by gaseous phase nitration of a hydrocarbon feed stock containing a small amount of carboxylic acids alone or in admixture with certain other oxygenated hydrocarbon compounds. The present process gives higher yields of nitroparaffins and a significantly higher percentage of the nitroparaffin in the form of nitromethane.
Processes to form nitroparaffins by gaseous phase nitration are known. U.S. Pat. Nos. 3,780,115 and 3,869,253 teach that nitration of saturated hydrocarbons higher than methane can be accomplished by contacting the hydrocarbon feed with nitrogen peroxide in the presence of oxygen, such as in the form of air, under elevated temperature and pressure conditions. The reactant gases are preheated and then introduced into the reaction zone where the gaseous phase nitration is carried out at elevated pressure and at elevated temperature. The gaseous effluent emitted from the nitration reaction zone is rapidly quenched. The quenched mixture then enters a separator where the gaseous materials are removed for subsequent purification and recycling and the remaining organic and aqueous phase liquid materials are separated by decantation and the nitroparaffins are recovered by distillation. This nitration process yields a mixture of products having a predominance of nitropropanes.
French Publication No. 78/32,118 discloses that the nitroparaffins product mixture can be made to have an increased yield of nitromethane, the most commercially desired product, by utilizing ethane as the hydrocarbon feed in the homogeneous gas phase nitration. The nitration process can be further enhanced by recycling into the hydrocarbon feed some of the nitropropane product and/or by conducting the nitration in the presence of an inert gas such as nitrogen, hydrogen or argon.
U.S. Pat. No. 4,260,838, similar to the above French reference, teaches that the gas phase nitration process of U.S. Pat. Nos. 3,780,115 and 3,869,253 can be improved by altering the feed stock to obtain suitable percentages of different nitroparaffins as suits the needs of the marketplace. This patent teaches that the feed stock be made up of a mixture containing propane, preferably recycled nitroparaffin and possibly inert gas and/or another alkane. The nitrating agent can be either nitrogen peroxide or nitric acid.
Each of the conventional processes, such as those described in the above referenced patents, provides a nitroparaffin product mixture which is low in yield of nitroparaffin and/or low in yield of the most commercially desired compound, nitromethane.